Method for making a heat exchanger with flattened tubes, the heat exchanger, and tubes made thereby

ABSTRACT

An apparatus and method for making a heat exchanger tube ( 14 ) for a heat exchanger ( 10 ) in which a continuous insert ( 26 ), having convolutes transverse to the length of the tube are located into a continuous shell as the shell is being formed. After placing the insert ( 26 ) into the partially open shell, the shell is closed and sealed as it passes through a bonding device ( 64 ) to seal the longitudinal edges of the shell to each other and the insert to the internal walls of the tube. The continuous shell with the inserted fin insert is subsequently sliced to produce individual cooling tubes.

TECHNICAL FIELD

[0001] The invention is related to an apparatus and method for makingtubes for a heat exchanger and in particular to tubes having aconvoluted fin insert in which the convolutions are transverse to thelength of the tube.

BACKGROUND ART

[0002] The use of cooling tubes in heat exchangers having rectangular oroblong cross-sections such as taught by Wallis in U.S. Pat. Nos.4,595,135 and 4,971,240 are well known in the art. More recently, Wallisin U.S. Pat. No. 5,271,151 discloses the formation of a plurality ofparallel longitudinal flow paths within an oblong cooling tube.Alternatively, Dudley in U.S. Pat. No. 5,372,188 and Guntly in U.S. Pat.No. 4,998,580 disclose the use of inserts convoluted in a directionparallel to the length of the cooling tube to form the plurality ofparallel longitudinal fluid flow paths called turbulators within thecooling tubes, while Study in U.S. Pat. No. 5,456,006 describes a methodfor inserting a turbulator into the cooling tube during the formation ofthe cooling tube. In the above cooling tubes the turbulators form smalllongitudinal flow paths extending parallel to the length of the coolingtube. This configuration is well adapted to charge air coolers.

[0003] In an alternate configuration of the cooling tube, Bae in U.S.Pat. No. 5,771,964 teaches a cooling tube in which small fluid flowchannels are provided transverse to the length of the cooling tube. Thistype of geometry produces a more efficient heat exchanger.

[0004] Against this background, the need has arisen for cost-effectivemanufacture of extruded tubes used in heat exchanging, i.e., condensing,applications. One requirement for instance, of refrigeration condensersis to supply the largest surface area to the compressed gases and beable to contain high internal (and often varying) pressures withoutdistortion or leak.

DISCLOSURE OF INVENTION

[0005] The invention is an apparatus and method for inserting ahigh-density insert such as a fin, into a tube having an oblongcross-section as the tube is being formed. The high-density insert incooperation with the internal surfaces of the tube forms a plurality oftransverse fluid paths.

[0006] The disclosed invention includes the utilization of a highdensity insert, having convolution counts well above the normal thirtyconvolutions per inch. Such an insert provides enhanced surfacesrequired for superior heat transfer characteristics. The disclosedinsert is bonded to the inside of a heat transfer tube, wherein itoffers a long, tortuous path which is conducive to efficiency of heattransfer. The enhanced insert may or may not have any louvers, as iscustomary in air side fins conventionally manufactured.

[0007] The disclosed structure provides a high internal strength whichretains high pressure. Strength is provided by bonding the insert to theinterior surface of flattened oval tubes. The disclosed sinusoidalinsert supports internal forces that define a truss-type form, therebypresenting a stiff construction. If brazed, the form of the convolutionsafter they are compressed, defines cavities which a molten clad fills,thereby forming a fillet bond.

[0008] An apparatus and for making a tube for a heat exchanger includesa first set of rollers to form a continuous longitudinal shell from ametal strip, and inserting a continuous insert into the shell as theshell becomes closed. The insert has high density convolutes transverseto the length of the continuous shell. Optionally, the insert issupported within the shell by a series of dimples. The continuous shellwith the insert is closed, and then bonded to seal the open edges of thestrip to each other as it passes through a bonding device (preferably aninduction heater). The method concludes with the slicing the sealedcontinuous tube into individual segments to produce desired lengths ofcooling tubes.

[0009] An object of the invention is to make a tube for a heat exchangerincluding an insert having high density of convolutions transverse toits length.

[0010] Another object of the invention is the addition of dimples in theouter shell to locate (preferably centrally) and support the insertinside the finished tube.

[0011] Still another object of the invention is to provide detents inthe outer shell from blocking the fluid channels formed in the sealedshell on opposite sides of the insert to form a serpentine fluid paththrough the cooling tube.

[0012] Another object of the invention is a method for making a tube inwhich the insert is loaded into the shell as the tube is being formed.

[0013] Still another object is to provide a cooling tube having superiorheat transfer properties.

[0014] Yet another object is to manufacture a cooling tube with a highdensity convoluted insert having convolutes transverse to the length ofthe tube.

[0015] A further advantage of the invention is that it is a costefficient way to fabricate uniform cooling tubes for heat exchangershaving an internal insert.

[0016] These and other advantages of the invention will become moreapparent from a reading of the Specification in conjunction with thedrawings.

BRIEF DESCRIPTION OF DRAWINGS

[0017]FIG. 1 is a perspective view of a heat exchanger incorporatingtubes made according to the invention.

[0018]FIG. 2 is a perspective view of the tube showing the fin insert.

[0019]FIG. 3 is a partially cut away perspective view of a tube showingthe convolutes of the fin insert.

[0020]FIG. 4 is a schematic of the tube mill apparatus according to theinvention.

[0021]FIG. 5 is a cross-section of the partially open shell, taken alongsection line 5-5 of FIG. 4.

[0022]FIG. 6 is a cross-section of the fin insertion wheel, taken alongsection line 6-6 of FIG. 4.

[0023]FIG. 7 is a cross-section of a closed metal shell after heating,taken along section line 7-7 of FIG. 4.

[0024]FIG. 8 is an alternate embodiment of the tube mill apparatus.

[0025]FIG. 9 is a perspective of a tube having dimples and detents.

[0026]FIG. 10 is a perspective of detent-forming rolls.

[0027]FIG. 11 is a perspective view of a tube mill apparatus for makingthe cooling tube of FIG. 12.

[0028]FIG. 12 is a perspective view of a partially open alternateembodiment of the tube.

[0029]FIG. 13 is a perspective view of the alternate embodiment afterbeing closed.

[0030]FIG. 14 is a cross-section of the fin insert having squareconvolutions.

[0031]FIG. 15 is a cross-section of a fin insert having a tear-dropconfiguration.

[0032]FIG. 16 is an end-view of an alternate embodiment of the tube inwhich a serrated insert is placed.

[0033]FIG. 17 is a perspective view of the insert depicted in FIG. 16,illustrating the direction of fluid flow thereacross and therethrough.

[0034]FIG. 18 is a part drawing of the insert depicted in FIGS. 16-17.

BEST MODES FOR CARRYING OUT THE INVENTION

[0035] The invention is an apparatus and method for making tubes for aheat exchanger 10 of the type shown in FIG. 1. The heat exchanger 10 hasa pair of spatially separated manifolds or headers 12 interconnected bya plurality of tubes 14. The tubes 14 may be arranged in a single rowtubes or two or more rows of cooling tubes as is known in the art.Preferably, cooling fins 16 are provided between adjacent cooling tubesto enhance the heat exchange between the cooling tubes and an externalatmosphere, such as air. The heat exchanger will normally have an inletconnector 20 attached to one of the headers 12 and an outlet connector22 attached to the opposite header 12.

[0036]FIG. 2 shows a first embodiment of the tube 14. The tube has anouter metal shell 24 having an oblong cross-section. Enclosed within themetal shell 24 is an insert 26 such as a high density convoluted fin,which forms a plurality of fluid paths generally transverse to thelongitude of the cooling tube 14. The insert 26 may have a simpleconvolute configuration as shown in FIG. 2, a square configuration asshown in FIG. 14 or an interlocking teardrop shape configuration inwhich adjacent sides of the convolutes touch each other as shown in FIG.15, or a serrated configuration as depicted in FIGS. 16-18. Preferably,the high density insert 26 has 40 or more (e.g. 40-100) convolutes perinch. The insert 26 is centered and internally supported within thecooling tube 14 by a plurality of dimples 28 provided in the outer shellalong opposite sides of the insert 26 as more clearly shown in FIGS. 3and 9-10.

[0037] The tube mill apparatus for making the cooling tube 14 is shownin FIG. 4 (preferred embodiment). Referring to FIG. 4, a metal strip 30from which the outer shell of the tube 14 is to be made is received froma reel 32 and guided into a tube mill apparatus 34 such as taught byWallis in U.S. Pat. No. 4,971,240. The tube mill apparatus 34 has afirst plurality of rolls 36 which progressively form the metal strip 30into the partially open clam shell form shown in FIG. 5. The apparatus34 may also optionally include at least one set of dimple forming rollsfor forming dimples in the shell 24 prior to placing the insert 26 intothe metal shell 24. The dimples serve to position the insert, ifdesired, centrally in the width of the tube. In this manner, the insertdoes not touch the internal radius of the flattened oval edges of thetube so that a passage is created for fluid flow. The dimple formingroll may be the first roll in the tube mill apparatus 34 or the dimpleforming function may be incorporated into any of the rolls of the firstplurality of rolls 36.

[0038] The dimple forming roll may also incorporate a punch or otherequivalent means for imparting blocker detents 40 in the metal strip 30at predetermined locations on opposite sides of the insert 26 along thelength of the cooling tubes (FIG. 10). The blocker detents 40 block thelongitudinal flow of the fluid along the longitudinal channels 42 and 44respectively formed between the internal surfaces of the metal tube 14and the sides of the insert 26 as shown in FIG. 9. The detents 40 formedalong the opposite sides of the metal shell 24 are staggered relative toeach other to produce a serpentine fluid path indicated by the arrow 46stretching from one end of cooling tube to the other.

[0039] Referring back to FIG. 4, a continuous high density fin insert 26is retrieved from a reel 48 and is guided to an insertion wheel 50 (FIG.6) which guides the fin insert 26 into the interior of the partiallyopen metal shell 24 prior to being closed. The insertion wheel 50 asshown in FIG. 6 has a pair of truncated conical outer portions 52 and 54extending radially from a cylindrical hub 56. The interior surfaces ofthe conical portions 52 and 54 form an annular slot 58 into which thefin insert 26 is received. The conical portions 52 and 54 engage andmaintain the separation of the edges of the metal shell 24 so that thefin insert 26 is accurately guided into the interior of the metal shell24 prior to the shell being closed. A guide roll 60 supports thepartially open shell 24 during the insertion of the fin insert 26, asshown in FIG. 6. The dimples 28 at the bottom of the metal shell (FIG.5) 24 support the insert 26 in its centered location until the shell isclosed. After the fin insert 26 is placed within the metal shell,closing rolls 62 close the metal shell 24 and the dimples 28 engage theinsert along opposite lateral sides and hold the insert in its desiredlocation as shown in FIG. 7. Returning to FIG. 4, after the metal shellis closed by the closing rolls 62, the closed assembly is heated(preferably by an induction heater 64) to a temperature sufficient tobraze or solder the lateral edges of the metal shell to each other andbraze the insert 26 within the closed shell. After brazing, a cutter 66cuts the brazed tube into desired lengths to form the individual coolingtubes 14.

[0040] An alternative embodiment 70 of the tube mill apparatus 34 formaking the cooling tubes 14 is shown in FIG. 8. As described above, ametal strip 30 from a roll 32 is fed into a tube mill apparatus 70 whichforms the metal strip into the clam shell configuration as previouslydiscussed.

[0041] A metal strip 72 from a reel 74 is formed into a continuouslength of a high density convoluted fin 26 by a set of rolls 76. Thehigh density fin 26 is convoluted to form fluid passages transverse tothe length of the metal shell. The fin 26 is inserted into the partiallyopen shell 24 prior to the shell being closed. An insertion wheel 78comparable to insertion wheel 50 is again used to place the high densityfin 26 into the partially open shell 24. Closing rolls (not shown) suchas closing rolls 62 will again close the metal shell 24 with the fin 26inside. A bonding device selected from group consisting of a heater, acontrolled atmosphere brazer (cab), an induction welder, a solderingdevice, an ultra sonic welder, and the like generally indicated by thereferenced 64 bond the closed metal shell to join the lateral edges ofthe metal shell to each other with the fin insert 26 inside. Formingrolls 36 form the metal strip 30 from a reel 32 into the outer shell 24as previously discussed.

[0042] The metal strips 30 and 72 are preferably made from an aluminumalloy coated with a brazing material or a solder having a meltingtemperature below the melting temperature of the aluminum alloy. Thethickness of the brazing material or solder layer is in the range from10% to 20% of the thickness of the aluminum alloy. Coated metal stripsas described above are readily available from several commercialsources. Although the preferred metal is an aluminum alloy, other coatedmetals which perform the same function are also commercially availableand may be used to make the outer shell 24 and the insert 26.

[0043]FIG. 12 shows an alternate embodiment 80 of the cooling tube 14for an automotive radiator. To make this embodiment, a coated metalstrip 82 is folded to form two leafs 84 and 86 (FIG. 13) which areclosed to form two parallel fluid channels 88 and 90. In these coolingtubes, inserts 92 and 94 comparable to insert 26 are disposed in each ofthe two fluid channels 88 and 90 forming a cooling tube 96 having twoparallel fluid flow channels.

[0044] The tube mill apparatus 100 for making this embodiment isillustrated in FIG. 11. In this tube mill apparatus, two strips ofcoated metal 102 and 104 from reels 106 and 108 are guided through afirst set of fin rolls 110 to form two parallel high density fin inserts112 and 114 respectively.

[0045] A third coated metal strip 116 from a reel 118 is formed by a setof tube forming rolls 120 which incrementally form the metal strip 116into the form shown on FIG. 12. Prior to folding the leafs 84 and 86 tothe closed position the two high density fin inserts 102 and 104 arelaid on the base portion 102 of the partially formed tubes as shown onFIG. 11. As discussed relative to the embodiment shown on FIG. 3,dimples, such as dimples 28, are used to centrally locate the fin insert102 and 104 respectively in the two fluid flow channels 88 and 90. Thetube closing roll 122 will then close the leafs 84 and 86. The tube withthe inserted fin inserts 102 and 104 is then heated such as heater 64(FIG. 4) to a temperature sufficient to braze or solder the longitudinalends of the two leafs 84 and 86 to the base portion 82 and fuse the fininserts 102 and 104 inside the fluid flow channels to form a continuousintegral assembly 124. A cutter such as discussed earlier will then cutthe continuous integral assembly 124 to form the desired cooling tube80.

[0046] The pear-shaped, or tear-shaped form of insert (FIG. 15) definesclosed chambers extending laterally in relation to the length of eachflattened tube. These chambers tend to confine the molten clad so thatit adheres to the walls of the tube and to the points of tangencybetween ridge lines of convulsions and the internal tube walls. Theclosed chambers serve to arrest the flow of molten clad away from thebonding site, thereby promoting strength and ability to withstand highinternal pressures.

[0047] In some embodiment of the disclosed manufacturing apparatus ormethod steps, no dimples or spacing members are required to position theinsert within the oval tube. For example, the insert may effectively bepositioned by an interference fit therewithin. Alternatively, a physicalseparator, such as a spacer blade can be interposed below the insert asit is placed edgewise into the clam-shell tube before closure.

[0048] FIGS. 16-18 depict a serrated form of insert which has acomponent of resistance to flow in the form of ridges R-R (FIGS. 17-18)which lie orthogonally to the direction of fluid flow.

[0049] While embodiments of the invention have been illustrated anddescribed, it is not intended that these embodiments illustrate anddescribe all possible forms of the invention. Rather, the words used inthe specification are words of description rather than limitation, andthat various changes may be made without departing from the spirit andscope of the invention.

What is claimed is:
 1. A tube mill for making flattened tubes for use ina heat exchanger, comprising: first set of rolls for continuouslyforming a first metal strip into a partially open continuous shell; aninsertion member disposed downstream of the first set of rolls, theinsertion member serving to locate a continuous insert into thepartially open continuous shell, the insert having at least oneconvolution in a direction transverse to the length of the continuousshell; and closing rolls downstream of the insertion member for closingthe partially open continuous shell around the insert and forming aclosed tube.
 2. The tube mill of claim 1 further including a cutterlocated downstream of the heater for cutting the closed sealed tube intodesired lengths.
 3. The tube mill of claim 1 further including at leasta second set of rolls for imprinting dimples into the metal strip whileit is being formed into the partially open continuous shell.
 4. The tubemill of claim 1 wherein parallel fluid flow passages are formed onopposite sides of the insert, the tube mill further including a punchfor imparting detents in the continuous shell to alternately block thefluid flow passages on opposite sides of the insert in a staggeredsequence to define a serpentine fluid flow path through the tube.
 5. Thetube mill of claim 4 wherein the rolls for imprinting dimples anddetents in the metal strip are incorporated in the first set of rolls.6. The tube mill of claim 1 further including one or more insertionmembers for inserting a subsequent insert into the partially opencontinuous shell, the convolutions of each insert being transverse tothe length of the continuous tube.
 7. The tube mill of claim 1 whereinthe first metal strip and continuous fin insert are coated with abrazing material and the heater heats the continuous shell to atemperature sufficient to braze the longitudinal edges of the continuousshell to each other and the fin insert to the internal surfaces of theclosed continuous tube.
 8. The tube mill of claim 1 wherein the firstmetal strip and the insert are bonded to each other so that thelongitudinal edges of the continuous shell are joined to each other andthe insert is joined to the internal surfaces of the closed continuoustube.
 9. The tube mill of claim 1 wherein the first metal strip and fininsert comprise a base metal strip coated with a layer of metal having amelting temperature lower than the melting temperature of the base metalstrip.
 10. The tube mill of claim 1 wherein the first set of rolls formsa partially open continuous shell which when closed forms at least oneinternal longitudinal fluid flow channel.
 11. The tube mill of claim 10wherein the at least one fluid flow channel comprises two side by sidecontinuous fluid flow channels, and said insertion mechanism places arespective one insert into each of said two fluid flow channels.
 12. Thetube mill of claim 1 wherein the convolutions of the fin inserts have aserrated cross-section.
 13. The tube mill of clam 1 wherein theconvolutions of the insert have a tear drop cross-section in which theside walls of adjacent convolutions touch each other to define closedchambers that confine molten clad so that it adheres to the internalwalls of the tube, thereby localizing a bonding medium at a bondingsite.
 14. The tube mill of claim 1 wherein the fin insert is a highdensity convoluted insert having at least 40-100 convolutions per inch.15. The tube mill of claim 1 further including a bonding device selectedfrom a group consisting of a heater, a controlled atmosphere brazer(CAB), an induction welder, a soldering device and an ultrasonic welder.16. A method for making a tube for a heat exchanger comprising: forming,with a first set of rolls, a continuous partially open metal shell froma metal strip; placing a continuous insert into the continuous shell,said insert having a high density of convolutions extending in adirection transverse to the length of the continuous shell; and closingthe continuous metal shell around the fin insert with a set of closingrolls.
 17. The method of claim 16 further including slicing the sealedcontinuous shell with the fin insert fused inside to form a desiredlength of flattened tube.
 18. The method of claim 16 further includingimprinting dimples in the step of forming a continuous partially openshell.
 19. The method of claim 16 further comprising forming twolongitudinal channels between internal rounded edges of the sealedcontinuous shell and the edges of the insert, the method furtherincluding imprinting detents along the sides of the continuous shell,and alternately blocking the two longitudinal channels in a staggeredsequence to define a serpentine fluid flow through the cooling tube. 20.The method of claim 16 further including the step of passing a secondmetal strip through at least one set of fin forming rolls to form thecontinuous fin insert.